The present invention relates to a motor driving device provided with a decelerator which is called, for example, "Geared Motor".
In electric vehicles, if a motor is provided for the wheels respectively, the driving torque for the wheel can be independently controlled, causing an effective control at the time of performing a small turn or preventing slippage. Therefore, a study upon electric vehicles whose four wheels are independently driven has been progressed, resulting a various disclosures.
Hitherto, an electric vehicle such as fork-lift or golf-cart employes a wheel motor disposed to each wheel as driving means. Such wheel motor generally employs a motor integrally provided with a gear decelerating device. The reason for such employment lies in that a high efficiency and high speed type motor can be used as a low speed and large torque type motor by combining such motor and decelerator. In a usual electric vehicles, the wheels thereof are rotated at the number of revolution of substantially 1000 rpm, while a motor arranged to be rotated at 2000 rpm is employed by the above-described type of vehicles.
As a usual type of the motor which is integrally provided with the above-described type of gear decelerating device, a motor of the type is known which is constituted in such a manner that the electric motor and the gear decelerating device are formed as individual units and the thus-formed units are integrally coupled to each other. In such structure, the gear decelerating device is structured so as to realize several stepped deceleration by using an external gear thereof.
In electric vehicles, the wheels thereof tend to move vertically due to uneveness of the road or the wheels can be turned (steered) laterally when the vehicles are driven. Therefore, in a case where a motor driving device is respectively provided for the wheels, the motor driving device needs to be arranged not to be interfered with the wheels when the wheels are moved or turned as described above. As a result, the space for providing the motor driving device is involved to be limited. That is, the reduction of the size of the motor driving device is necessary. In order to satisfy such necessity, the size of the motor needs to be reduced as much as possible.
However, in the conventional motor which is integrally provided with the gear deceleration device, the electric motor and the decelerating device respectively comprises a heavy casing since the same are independently formed as units. Furthermore, the casing for the decelerating device cannot b reduced to a satisfactory size since it needs to accommodate a multiplicity of external gears. In addition, in such external geared decelerating device, since two gears are secured in the axial direction to one rotational shaft, the overall length thereof involves to be lengthened. Therefore, there is a limit to reduce the overall body size of the motor.
To this end, a structure can be considered to be employed which is constituted in such a manner that the electric motor and the gear decelerating device are accommodated within a casing. However, in the conventional motor which is integrally provided with the gear decelerating device, the rotational shaft for the motor and the rotational shaft for each of the decelerating steps are individually supported by a pair of bearings. In order to support these bearings, an wall for supporting the bearings needs to be provided in addition to the outer wall of the casing. Therefore, the shape of the casing can be complicated, and the overall length cannot be shortened to a satisfactory size. In addition, a problem arises that such bearings cause mechanical loss which can lead to a fact that the output torque is reduced.